Apparatus for vacuum die casting



Oct. 15', 1963 .1. c. MOORE APPARATUS FOR VACUUM DIE CASTING 3 Sheets-Sheet 2 Filedv March 12, 1958 FIG-4 INVE'IVTOR JESSE Q MO0RE A TTORNEYS Oct. 15, 11963 J. c. MOORE 3,1 06;755

APPARATUS FOR VACUUM :DII/E EASTI'NG Filed yuan-ch 1 2, 1958 :5 Sheets-Sheet is A TTUR/VEYS United States Patent 3,136,755 APPARATUS FER VACUUM DEE CASTENG Jesse C. Moore, Box 147, Fort Recovery, ()hio Fiied Mar. 12, 1958, Ser. No. 720,952 3 tjiaims. (Cl. 22-453) This invention rel-ates to die casting machines and to methods of operation thereof, and in particular is concerned with an improved method of die casting utilizing vacuum for evacuating the mold cavity.

=Die casting machines are well known and likewise it is known to employ vacuum for evacuating the cavity in which a casting is to be made for promoting the rapid filling of the cavity and to eliminate air pockets therefrom.

Heretofore, however, such systems have only been partially successful and effective and have generally been quite wasteful of the vacuum apparatus. Much difficulty has been encountered in exerting the vacuum ion the mold cavity without excess leakage of air about the cavity, and this has led to the practice of building enclosures about the die with the entire enclosure being evacuated in order to evacuate the cavity in the die. Systems of this nature are quite expensive and cumbersome and difiicult to install in many die casting vmachines and are not as efficient as could be desired in that the degree of evacuation of the die cavity is sometimes rather low.

Having the foregoing in mind, a primary object of the present invention is the provision of an improved method of utilizing vacuum in connection with die casting processes which leads to a much higher degree of evacuation of the die cavity than has heretofore been possible.

Another object of this invention is the provision of an improved method for vacuum die casting which can be applied to substantially any die casting machine at an expense much reduced over the expense of other types of vacuum systems.

A still further object of this invention is the provision of vacuum equipment and controls therefor adapted for being associated with die casting machines which leads to improved castings while making extremely efficient use of the vacuum apparatus.

Is is also an object of this invention to provide a novel control arrangement and a method of controlling vacuurn applied to a die cavity in a die casting machine that leads to results vastly improved over what can be obtained by conventional control arrangements.

A further object of this invention is the elimination of troublesome valving in either the molten metal or in the vacuum passages of the die proper, as has been the general practice heretofore in die evacuation systems.

These and other objects and advantages will become more apparent upon reference to the accompanying drawings, in which:

FIGURE 1 is a more or less diagrammatic representation of one type of die casting machine having associated therewith a die evacuating system according to the present invention,

FIGURE 2 is a vertical section taken through a typical die showing the vacuum connections thereto,

FIGURE 3 is an enlarged view showing the preferred form of seal about the parting line of the die,

FIGURE 4 is a view looking in at the face of the cover of the die as indicated by line 44 in FIGURE 2,

FIGURE 5 is a diagrammatic representation of the preferred control circuit for the application of the vacuum and the injection of the metal in the die casting machine,

FIGURE 6 is a fragmentary view showing another form which the seal about the parting line of the die can take,

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FIGURE 7 is a view showing a modified arrangement for connecting the vacuum conduit with the die,

FIGURE 8 is a sectional view similar to FIGURE 6 but showing a modified arrangement of the seal about the parting line of the die wherein the resilient element is carried by the ejector half of the die and is backed up by a strip of spring material,

FIGURE 9 is a sectional view showing how the seal could be placed about the parting line of the die where the exhaust passage is provided by forming a groove about the die thereby permitting the die and seal to occupy the minimum of space, and

FIGURE 10 is a fragmentary somewhat diagrammatic sectional View showing the application of the present invention to a cold chamber die casting machine and also illustrating the automatic filling of the chamber by utilizthe force of vacuum generated in the die cavity.

Referring to the drawings more in detail, the die casting machine in FIGURE 1 comprises a bed or frame part 16 that includes a stationary platen or bolster 12 to which is attached the cover 14- of a die, the other part 16 of which, known as the ejector, is carried on a movable platen 18 slidably mounted on rods 20.

A crucible 22 located Within an enclosure 24 is provided and heating means within the enclosure, such as gas burners, maintain the metal 26 within the crucible or pot in a molten state.

Extending into the molten metal is a cylinder 23 into which the molten metal flows via a passage 3%. A piston 32 is reciprocable in cylinder 28 for forcing the molten metal out the bottom thereof and up through a passage 34 into a sprue opening in die cover 14 and through which sprue opening the metal flows into the cavity of the die.

Piston 32 is connected with ram 36 that is connected with the piston of a double acting hydraulic motor 38 to which is connected conduits 4d and 42.

The cavity in the die is adapted for being evacuated by a conduit 44 that leads through a solenoid operated valve 46 to a vacuum accumulator tank or reservoir 43 to which is connected a vacuum pump 52 and which connection may include a check valve 56*.

Referring now to FIGURES 2 and 3 it will be noted that the die comprising the parts 14 and 16 defines a cavity 54 from which leads the sprue 56 that communicates with passage 34 previously referred to. The cavity 54 is communicated with the periphery of the die by shallow passages 58 extending from the cavity outwardly, as will be seen in FIGURE 4. These passages, which form vent slots for effecting the principal evacuation of the die cavity, may be on the order of about five thousandths of an inch deep and may be any suitable width.

The die according to the present invention is completely surrounded by a relatively small exhaust passage 64- terminating at one side of the die, preferably the top, in a chamber that communicates with the vacuum conduit 44. I

According to this invention the exhaust chamber surrounding the die is formed, as will be seen in FIGURES 2, 3, and 4, by a block or bar 6t) attached to three sides of one of the die parts, for example the ejector 16, and which block or bar is adapted for being closely approached, or even abutted by a bar 62 carried on the other part of the die, in this case the cover 14, so that a chamber 64 is defined about the parting line of the die. A spacer element 66 may be placed under bar 6'2 or may be integral therewith in order to space the bar 62 outwardly from the periphery of the die. The exhaust chamber may be cut in the die also if deemed practical for a certain application where the space limitations of the installation prevent placing the seals outwardly from the periphery of the die.

Sealing of the chamber 64 is obtained by having the block or bar 69 beveled as at 68 and which bevel is adapted for wiping engagement with a metal or rubber or rubbcrlike strip 70 clamped on bar 62 by clamp element 72.

The top of the die is provided with a pair of spaced clock elements 74 on ejector 16 and 76 on cover 14 that define therebetween a zigzag baflling passageway 78 that communicates at its ends with the chamber 64 extending about the parting line of the die and also with the vent slots that extend upwardly from the die cavity to the top of the die.

Passage 7 8 is adapted for communicating with vacuum conduit 44 and this is preferably by way of a filter element 80 which may be of sintered metal or ceramic.

A seal between the blocks 74 and 76 is accomplished by an upstanding transverse member 82 carried by one of the parts having its upper edge beveled and a sealing strip 84 on the other part adapted for wiping engagement with the said bevel edge. Strip 84 may be a continuation of the previously mentioned sealing strip 76 so that an eifective seal is established completely about the periphery of the die.

It will also be noted that the seal becomes eifective slighlty before the die parts meet, and that a minimum volume is enclosed about the die inside the sealing strip. This is important because it is required to evacuate only a small amount of ain from within the die and from about the die in order to obtain a high degree of evacuation of the die cavity.

It will also be noted that the seal strips are of such a nature, in being supported on the inside, that they will not tend to collapse inwardly even though an extremely high vacuum is created within the mold cavity and within chamber 64 and passage 78.

The wiping action of the seal strips against the sealing surface provided for engagement by the sealing strips is operable to establish a highly efiicient seal which tends to remain clean at all times. Further, considerable latitude is permissible in the degree of closing of the die and a highly effective seal will still be had. Thus, if small metal particles or dust accumulate on the mating faces of the die parts so that the die parts are held apart a few thousandths of an inch, this usually being the case, no loss of efilciency of sealing about the parting line of the die will occur.

The provision of the bafile passage 78 prevents molten metal injected into cavity 54 from getting into the vacuum passageway. Normally, the metal will be chilled and set up within the vent slots so that only a small flash about the cast article will be present, but in case the metal runs completely through the vent slots, it will be chilled within passage 78 so that it does not get into the vacuum system.

Similarly, the filter S is effective for eliminating dust and extremely fine metal particles from the vacuum system. This filter could, in many cases, be eliminated but it is generally preferred for the filter element to be present and preferably in a relatively large size to permit rapid how of air therethrough.

Any metal that may flash outwardly between the die parts will be delivered into chamber 64 and will impinge against block or plate 62 and will be chilled immediately so that when the die is opened, this metal flash will either drop from chamber 64 or can readil be removed therefrom. Such metal flash will be prevented from striking the seal strips so that the seal strips are thus prevented from being burned and will have extremely long life.

FIGURE illustrates a preferred type of control system and in this view it will be noted that there is provided a. ram 90 operating through a toggle mechanism 92 for closing the die parts. When the die parts are completely closed ram 90 engages a limit switch LS that has one side connected to power line L1 and its other side connected to one side of each of two adjustable microsecond timers 4 T1 and T2, the other sides of which are connected with the other side of the power line, L2.

Timer Tl controls, either directly or via a relay, a blade 94 that is in series between power lines L1 and L2 with solenoid S1 of the vacuum control valve 46.

Timer T2 controls a blade 96 that is connected in series between power lines L1 and L2 with solenoid S2 pertaining to the valve 98 that controls the supply of fluid to motor 38 that operates shot piston 32.

A selector switch 100 may be provided in the circuit to solenoid S1 so that the machine can be operated without using the vacuum attachment, if so desired.

In operation, the timing of the application of vacuum to the mold cavity and the operation of the shot piston is most important. The shot piston is timed out so that the molten metal is injected into the die cavity when the highest degree of vacuum exists therein. The particular time will vary slightly from one die to another. Timer T2 is generally set to give a shot delay on the order of about three tenths of a second, plus or minus, after the blade 94 of timer T1 is closed. This is an average condition which will bring about the injection of the metal into the cavity at the time the cavity is evacuated to the highest degree and before molten metal is drawn by vacuum into the die impression. The shot delay time setting thus takes into account the machine shot mechanism response time lag.

As soon as the metal is injected into the die cavity and has it completely filled, the need for the vacuum is eliminated and timer T1 accordingly is adjusted to then open its blade 94. The adjustment of dwell timer T1 is not critical but is adjusted so as to close the vacuum valve just after the time the die cavity is filled and rammed to the final squeeze that will produce a dense, high quality casting. This time duration may amount, for example, to 1%. seconds, more or less, from the time the valve 46 is opened.

This arrangement makes highly economical use of the vacuum and also permits the accumulator to build up to the proper degree of vacuum before the next operating cycle of the die casting machine. The cycling of the machine can thus be quite rapid without there being any reduction in the degree of the vacuum available for evacuating the die on each cycle. This maintaining of a high degree of vacuum in the accumulator is further augmented by the extremely small volume that must be evacuated according to the present invention as opposed to the large volumes that must be evacuated in conventional systems where an enclosing box is built about the die.

The high degree of vacuum available and the small volume being evacuated permits an extremely high degree of evacuation of the die cavity and the continuing of the evacuation throughout the filling cycle of the cavity with the advantages referred to above obtaining in that the recovery of the desired degree of vacuum in accumulator 48 is extremely rapid.

For example, where conventional die evacuating systems may develop a vacuum of 15 inches of mercury within the enclosure around the die, actual measurements taken within the die cavity of the present system have indicated evacuations of better than 24 inches of mercury.

By utilizing the system of the present invention, it is possible to produce castings having less scrap than by conventional practices or by other vacuum techniques and while it is also possible at the same time substantially to reduce the casting wall thickness, in some cases of up to 50% without detracting from the quality of the casting Where strength is not a primary consideration. Where strength is a consideration, the casting wall thickness can be reduced somewhat because the method of the present invention produces more dense castings than have heretofore been produced and completely eliminates voids and air pockets.

FIGURE 6 illustrates an arrangement wherein a metal seal strip 102 is employed which is formed so as wipingly to engage a bevel 104 on the die part against which it is to seal. A recess 1% extending about the parting line of the die provides the chamber which is evacuated when the machine is operated. The efiiciency of sealing of the FIGURE 6 arrangement is less than that of the preferred embodiment described above but due to the close timing of the cycle of the machine, the FIGURE 6 modification is found to be satisfactory in a great many cases and will permit a high degree of evacuation of the die cavity.

FIGURE 7 illustrates a slightly modified arrangement for connection of the vacuum conduit 108 with the chamber 110 extending across the top of the die. In FIGURE 7 chamber 110 is formed by the member 112 attached to die cover 114 and with member 112 having a lip turned downwardly at 116 so that flash from the die cannot directly enter conduit 1118.

A seal strip 118 carried 011 die ejector 12ft is adapted for sealing against a projection on member 112 and there may be a filter strip 122 provided for filtering the air as it passes from chamber 110 into conduit 108.

In FIGURE 8 the cover 121} of the die canies the beveled bar 122 While the ejector 124 carries the resilient strip 126 that engages the beveled end of bar 122. The resilience of the strip 126 is maintained by a thin strip of spring steel or other spring material 123 on the opposite side thereof from bar 122. The arrangement of FIGURE 8 insures that the resilient strip 126 will be separated from the die cover so that it will be less likely to be struck by ejected parts or by hot drippings whereby the life of the strip is considerably lengthened.

In FIGURE 9 there is illustrated an arrangement wherein the die 1% has the exhaust groove of chamber 132 about the parting line thereof formed by cutting a groove into the die so that the seal elements 134 will project outwardly beyond the die a minimum anrount thereby permitting the present invention to be utilized where space limitations do not permit the die to carry the seal outwardly beyond the limits thereof any substantial amount.

The application of the present invention to a cold chamber die casting machine is diagrammatically illustrated in FIGURE wherein the ejector 140 is mounted on a movable platen 142 while the die cover 144 is mounted on a stationary platen 14-6.

Seal means as already described extend about the parting line of the die as at 148 and there is connected to the die conduit 151 leading to a vacuum accumulator via a solenoid controlled valve as described in connection with FIGURES l and 5.

In the cold chamber machine a cylinder 152 forming the cold chamber extends through the cover and stationery platen and has reciprocable therein the injection plunger 154. When the injection plunger is retracted, as is illustrated in FIGURE 10, the upper end of a feeder or fill tube 156 is exposed, this tube extending from cylinder or chamber 152 downwardly into the molten metal in pot 158.

The arrangement is such that, by proper timing of the delay between the application of suction to the die and the initiation of the advancing movement of injection plunger 154, there will be drawn upwardly through feeder tube 156 and into chamber 152 an amount of molten metal sufficient for filling the die cavity and the gates and runners pertaining thereto. It will be evident that the arrangement of FIGURE 10 lends itself well to workability for the feeder tube is relatively short and offers little restriction to the passage of metal therethrough.

The extremely high degree of evacuation of the die cavity will also evacuate the chamber and feeder tube and cause the molten metal to rise into the chamber. By suitable adjustment of the delay timer that controls the shot, the initiation of movement of injection plunger 154 can be controlled so that a controllable amount of molten metal will be transferred into the chamber and then injected into the die cavity.

The plunger 154 will be seen to have a head portion scribed modification and may be outlined in brief as follows:

-(1) The operator commences the cycle which causes the die to close and lock up.

(2) When the die locks up and closes the lockup switch, the vacuum valve opens which causes rapid evacuation of the die and the cold chamber thereby causing molten metal to be drawn into the chamber.

(3) The adjustable shot delay timer (which was energized at the same time as the solenoid actuated vacuum valve) delays the shot until a predetermined amount of metal is drawn into the chamber and then the shot is made. The molten metal is thus shot into a highly evacuated die cavity and the evacuation of the die continues to remove residual air and gases from the die throughout the filling operation.

(4) As the shot plunger advances past the feeder tube opening it relieves the suction therein and the molten metal in the feeder tube flows downwardly into the melting pot.

(5) Just after the shot piston has filled the die and rammed the metal, the vacuum dwell timer setting runs out and the vacuum valve closes.

(6) The die is then opened, either by the operator or by a suitable timer, and the shot piston pushes out the biscuit of surplus metal and the entire casting rides the traveling ejector.

(7) About the time the die is completely opened the casting is ejected and the shot piston retract-s, thus completing the cycle.

In connection with the cold chamber machine of FIG- URE 10, it may occur that the level of the molten metal in pot 158 will drop sufliciently to change the amount of material drawn into the chamber to the extent that improper castings will be produced. With this in mind, there may be associated with the pot some means of maintaining the liquid level therein substantially constant. This could take the form of an automatic feed or some automatic means for raising and lowering the pot itself.

For the sake of simplicity, a simple device for adjusting the pot level is illustrated. This comprises a bracket 17G attached to the pot which is connected with ram 172 of a hydraulic motor 17 4. Connected with hydraulic motor 174- is a reversing valve 176, preferably a four-way closed center valve, which has a valve member connected by a rod 178 with a float 180 that floats on the molten metal in pot 158. Whenever the level of the molten metal in pot .158 changes, the float will move to follow the changing level and adjust the valve member of valve 176 so as to actuate ram 172 and therethrough bracket 171) and pot 158 to move the pot in a direction to return the float to its initial position whereby the level of the molten metal is automatically maintained substantially constant at all times.

The present invention has been specifically illustrated and described in connection with hot :and cold chamber die casting machines wherein molten metal is injected into a die cavity, but it will be understood that the same process and operating cycle and substantially the same structure could be employed to advantage in connection with the molding of other materials, particularly plastics and specifically those plastics which become extremely thin upon being heated to molding temperature.

It will be understood that this invention is susceptible to modification in order to adapt it to different usages and conditions; and, accordingly, it is desired to comprehend 7 such modifications within this invention as may fall within the scope of the appended claims.

I claim:

1. In a vacuum assisted die casting machine including stationary and movable die members which join along a parting line and have cooperating faces which define a die cavity, a gate for delivering molten metal to the cavity, and a vacuum pump for evacuating the cavity and the gate, the improvement which comprises a parting line trap chamber formed in the mating faces of the die members; an outlet port formed in a wall of the chamber for connecting it with the vacuum pump; a shallow parting line vent passage defined by the mating faces of the die members for providing continuous communication between the die cavity and the trap chamber; a bafile means located in the trap chamber adjacent the path of travel of the metal entering that chamber through the vent passage and provided with a surface that intersects the plane of said passage; and means rendered effective when the die members are closed for sealing the parting line and thus preventing air from entering the die cavity, the :gate, the vent passage and the trap chamber when these spaces are evacuated.

2. In a die casting machine; closable die parts adapted for defining a die cavity when closed, means associated with said die parts defining a chamber relatively small in cross section extending about three sides of the die when closed, said means comprising cooperating elements of a seal to seal off the chamber from the atmosphere, means on the other side of the die defining a somewhat larger chamber communicating at its ends with the first mentioned chamber and said larger chamber also being sealed from the atmosphere, a source of vacuum, means for connecting the source of vacuum with said larger chamber for evacuating the chambers and cavity, there being means communicating the cavity with the chambers, and means for injecting molten metal into the die cavity when the said cavity is evacuated, said larger chamber being defined by blocks carried by the respective die parts and said blocks forming therebetween a zigzag passageway whereby flash from the die is entrapped within said larger chamber, said blocks separating when the die parts are separated whereby such flash is discharged from said larger chamber, and there being a filter element of substantial size interposed between the suction connection to said larger chamher and sealed zigzag passageway.

3. In a die casting machine; separable die parts adapted for being closed to define a die cavity, cooperating elements of a seal carried by the die parts adapted for forming a seal about the parting line of the die when the die parts are closed, there being a chamber of relatively small cross section extending about the die inside the seal, a plurality of distributed passages in the die connecting the chamber with the die cavity, a source of vacuum of substantial size, a conduit of substantial size connecting the source of vacuum with said chamber, a normally closed solenoid valve in said conduit, power means for closing said die parts, a switch operated into closed position in response to the closing of the die parts, and timer means responsive to the closing of said switch for first energizing said solenoid valve to cause rapid evacuation of the chamber and die cavity and thereafter, after a predetermined short time delay, to cause injection of molten metal into the die cavity, said timer means also being responsive to a still further time delay for deenergizing said solenoid valve, there being baflle means in said chamber interposed in the path of gas flow to said conduit to prevent metal from entering the conduits.

References Cited in the file of this patent UNITED STATES PATENTS 1,013,548 Grey Jan. 12, 1912 1,056,442 Parkhurst Mar. 18, 1913 1,488,545 Kadow Apr. 1, 1924 1,717,607 K-adow June 18, 1929 1,717,608 Kadow June 18, 1929 2,195,360 Daesen Mar. 26, 1940 2,209,882 Galloway July 30, 1940 2,243,835 Brunner June 3, 1941 2,304,461 Knowles Dec. 8, 1942 2,401,491 Lyons June 4, 1946 2,515,654 Kalina July 18, 1950 2,637,882 Plott May 12, 1953 2,660,769 Bennett Dec. 1, 1953 2,774,122 Hodler Dec. 18, 1956 2,864,140 Morgenstern Dec. 16, 1958 2,971,230 Coleman Feb. 14, 1961 3,006,043 Goldhamer Oct. 13, 1961 3,019,495 Cornell Feb. 6, 1962 

1. IN A VACUUM ASSISTED DIE CASTING MACHINE INCLUDING STATIONARY AND MOVABLE DIE MEMBERS WHICH JOINT ALONG A PARTING LINE AND HAVE COOPERATING FACES WHICH DEFINE A DIE CAVITY, A GATE FOR DELIVERING MOLTEN METAL TO THE CAVITY, AND A VACUUM PUMP FOR EVACUATING THE CAVITY AND THE GATE, THE IMPROVEMENT WHICH COMPRISES A PARTING LINE TRAP CHAMBER FORMED IN THE MATING FACES OF THE DIE MEMBERS; AN OUTLET PORT FORMED IN A WALL OF THE CHAMBER FOR CONNECTING IT WITH THE VACUUM PUMP; A SHALLOW PARTING LINE VENT PASSAGE DEFINED BY THE MATING FACES OF THE DIE MEMBERS FOR PROVIDING CONTINUOUS COMMUNICATION BETWEEN THE DIE CAVITY AND THE TRAP CHAMBER; A BAFFLE MEANS LOCATED 